The neovascular eye diseases retinopathy of prematurity, proliferative diabetic retinopathy, and wet age- related macular degeneration are major causes of blindness through the lifespan. There is thus a critical need to find novel cellula components that could be targeted to block ocular neovascularization. Ferrochelatase (FECH) is one such component, the target of an antiangiogenic compound selective for microvascular endothelial cells. FECH is responsible for inserting ferrous ion into protoporphyrin IX, the final step in heme biosynthesis. Intriguingly, FECH is necessary for proliferation of ocular endothelial cells in vitro and in vivo in the laser-induced choroidal neovascularization (L-CNV) and oxygen-induced retinopathy (OIR) models. The long-term goal is to elucidate the role of FECH in angiogenesis, define why endothelial cells are particularly sensitive to its loss, and develop novel therapies targeting this protein or its pathway(s). The rationale for this research is that FECH is a significant mediator of angiogenesis, a target of an antiangiogenic small molecule, and a previously unappreciated regulator of key angiogenesis factors including hypoxia-inducible factor 1?, mitochondrial Complex IV, heme oxygenase 1 (HO-1), and nitric oxide synthases (NOS). The objective in this application is to determine how FECH functions as a regulator of angiogenesis. The overall hypothesis is that FECH activity and the synthesis of hemoproteins are required for ocular angiogenesis and that reducing the levels of FECH will prevent ocular angiogenesis. Guided by strong preliminary data, the hypothesis will be tested via three specific aims: 1. Determine a) the temporal and spatial expression of FECH and its substrate protoporphyrin IX in human proliferative diabetic retinopathy and CNV specimens and in mouse OIR and L- CNV models and b) the environmental cues that increase FECH expression/activity. FECH expression will be assessed in disease samples and over a timecourse in OIR and L-CNV models, then the factors that regulate FECH will be dissected, including hypoxia and reactive oxygen species. 2. Determine which FECH-modulated signaling pathway(s) (nitric oxide, Complex IV, HO-1) are key to angiogenesis. The effect of loss of FECH on Complex IV, HO-1, and NOS expression, hemylation, and function will be tested, and other endothelial hemoproteins sensitive to FECH loss will be identified by hemoproteomics. 3. Evaluate the efficacy and potency of a novel small molecule FECH inhibitor in ocular angiogenesis. Novel compound SH-11037 will be shown to interact with FECH, then tested in the OIR and L-CNV models and the effects on hemoproteins assessed. This work is innovative, as it is the first mechanistic study of the role of FECH in angiogenesis. It will also be the first analysis of the role of protein hemylation in regulation of ocular angiogenesis, the first application of hemoproteomics in angiogenesis research, and the first examination of FECH inhibition as a therapy. The work is highly significant because it will define FECH as a new angiogenic mediator and determine its regulation and downstream effects, leading to development of new ways to prevent blindness.